1. Field of the Invention
The present invention relates to an organic electroluminescence element (also referred to as xe2x80x9corganic EL elementxe2x80x9d hereinafter) utilizing an organic compound material which exhibits an electroluminescence phenomenon, i.e., emission of light resulting from injection of an electric current into the organic material and to a method of manufacturing the same.
The present invention also relates to an organic electroluminescence display device (also referred to as xe2x80x9corganic EL display devicexe2x80x9d hereinafter) comprising a plurality of organic EL elements.
2. Description of the Related Art
In recent years, much attention has been focused on the organic EL display device with a flat display panel on which many organic EL elements each comprising an organic light-emitting layer made of an organic material are arranged. In general, as shown in FIG. 1, each organic EL element 1 has such a structure that a transparent electrode 3 (anode) made of indium tin oxide (so called ITO), a plurality of organic functional layers 4 made of respective organic materials and including the organic light-emitting layer, and a metal electrode 5 (cathode) are sequentially laminated on a glass substrate 2 serving as a display surface, by vapor deposition or the like. The organic functional layers 4 may include a hole injection layer, a hole transport layer, an electron transport layer and the like if necessary in addition to the organic light-emitting layer. The hole injection layer is made of an organic material capable of injecting positive holes into the hole transport layer. The hole transport layer is made of an organic material capable of transporting positive holes into the organic light-emitting layer. The electron transport layer is made of an organic material capable of transporting electrons into the organic light-emitting layer. For example, there is an EL display device of the X-Y matrix type in which EL elements are manufactured in such a manner that the hole transport layer and the organic light-emitting layer are deposited in that order on ITO stripes of transparent electrodes (anode lines) previously formed on a transparent glass substrate and then a plurality of metal electrodes (cathode lines) are formed on the organic light-emitting layer so as to cross the ITO stripes on two levels. The respective EL elements at intersections between the anodes and cathodes form a matrix of light-emitting points corresponding to pixels. In addition to the EL element with a two-layered structure composed of the hole transport layer and the organic light-emitting layer above mentioned, there are other EL element types such as a three-layered structure having an organic electron transport layer additionally provided between the organic light-emitting layer and the metal electrodes, and a multiple-layered EL element type formed of still more layers.
Since the vapor depositions of the individual layers on the glass substrate are preformed for making the organic EL element, for example as shown in FIG. 2, if dust or a solid foreign body 6 lies on the anode 3 at the time of depositing those layers, the foreign body makes it hard for the following vapor particles to be vapor-deposited around the underlying contact on the anode. It is therefore probable that an organic functional layer 4 tends to be thinner at the peripheral portion of the area underlying the foreign body than at the other areas. As a result, the anode 3 and a cathode 5 to be stacked later come closer to each other in the vicinity of the foreign body 6, thereby causing concentration of an electric field which will change the luminance of the emitted light. In some case, the anode 3 may come into contact with the cathode 5 thereby causing short-circuiting, which may produce non-luminous areas called xe2x80x9cdark spotsxe2x80x9d or may damage the EL element per se.
One countermeasure that has been taken against this problem is to clean the substrate upon deposition of each layer. However, this method alone is hardly possible to completely remove a foreign body once it is stuck on any layer.
The present invention has been made in view of the above circumstances, and an object thereof is to provide a reliable EL element in which the possibility of a short circuit or leak current between the transparent electrode anode and the metal electrode cathode is reduced.
To attain the above object, the present invention provides an organic EL element comprises:
a substrate carrying a transparent electrode;
a plurality of organic functional layers including an organic light-emitting layer deposited on the transparent electrode, wherein a part of at least one of the organic functional layers which is heaped on a solid foreign body is melted, regardless of whether or not the solid foreign body has been on the transparent electrode, so that the melted part of the organic functional layer on the solid foreign body is merged into the organic functional layer stacked on the transparent electrode around the solid foreign body, thereby burying the solid foreign body in the organic functional layer; and
a metal electrode over the organic functional layers.
In the organic EL element according to the invention, the melting of the part of the organic functional layer covering the solid foreign body is performed in a way that the whole substrate is heated to a temperature equal to or higher than a glass transition point of the organic functional layer and equal to or lower than a melting point thereof.
To attain the above object, the present invention also provides a method of manufacturing an organic EL element having a plurality of organic functional layers including an organic light-emitting layer sandwiched between a pair of electrodes, which method comprises the steps of:
depositing a first organic functional layer over a transparent electrode previously formed on a light permeable substrate;
melting a part of the first organic functional layer which is heaped on a solid foreign body, regardless of whether or not the solid foreign body has been on the transparent electrode prior to the first organic functional layer forming step, so that the melted part of the first organic functional layer on the solid foreign body is merged into the first organic functional layer stacked on the transparent electrode around the solid foreign body, thereby burying the solid foreign body in the first organic functional layer;
depositing a second organic functional layer on the first organic functional layer; and
forming a metal electrode over the second organic functional layer.
In the method of manufacturing an organic EL element according to the invention, the step of melting the part of the organic functional layer covering the solid foreign body is performed in a way that the whole substrate is heated to a temperature equal to or higher than a glass transition point of the organic functional layer and equal to or lower than a melting point thereof.
In the method of manufacturing an organic EL element according to the invention, the organic functional layers and the metal electrode are formed through a vapor deposition method.
According to the EL display device having the above construction, even if dust or a solid foreign body is inadvertently introduced during the manufacturing process of the organic EL element, the foreign body is always enclosed by organic material i.e., an organic functional layer, so that the transparent electrode and metal electrode of the organic EL element are always set apart at a predetermined distance from each other, thus preventing the transparent electrode and the metal electrode from coming close to or contacting each other. Even if a foreign body is adhered to the transparent electrode, it is possible to prevent generation of a leak current between the transparent electrode and the metal electrode thereby preventing reduction in the luminance of light emitted from each organic EL element and preventing the organic EL elements from being damaged.